1. Field of the Invention
This invention relates to biological tissue cutters for use with atherectomy devices inserted into a biological conduit for removal of diseased tissue, and specifically relates to cutters adapted for removal of both calcified soft tissue.
2. Previous Art
Atherosclerosis is a condition characterized by fatty deposits (atheromas) in the intimal lining of a patient's blood vessels. Atherosclerosis can present in a variety of ways including angina, hypertension, myocardial infarction, strokes, and the like. Regions of the blood vessel which are blocked by atheroma, plaque, or other material are generally referred to as stenoses, and the blocking material as stenotic material. The atheromas deposited on the blood vessel walls are often relatively soft and tractable. However, in many cases the atheromic material is a calcified and hardened plaque. Removal of the calcified tissue by current atherectomy is extremely difficult.
Atherectomy is a procedure which has been developed for removing stenotic material from the vascular system, usually before substantial calcification has occurred. Atherectomy procedures utilize a variety of special catheters having tissue cutting members (cutters) located at a distal end. In use, the catheter is inserted into a biological conduit of the vascular system so that the cutter is adjacent to the stenotic region. The cutter is then manipulated to excise a portion of the stenotic material. The severed material is captured to prevent the release of emboli into the blood stream.
The tissue cutting member on an atherectomy catheter can take a variety of forms, including fixed blades (requiring movement of the entire catheter to effect cutting) and movable blades which are manipulated within a stationary housing at the distal end of the catheter.
Of particular interest to the present invention are atherectory catheters of the type described in copending U.S. continuation-in-part application, Ser. No. 08/091,160, filed Jul. 13, 1993 by Milo et al., entitled "Imaging Atherectomy Apparatus," hereby incorporated by reference. These atherectomy catheters include a cutter housing attached to the distal end of a torquable catheter body. A circular cutting blade is disposed within the housing and is secured to the distal end of a rotatable drive shaft (torque cable). "Torque cable" is a general term in the art which refers to any means used to rotate and advance the cutting blade of the catheter. An elongated aperture (window) formed along one side of the housing allows the intrusion of stenotic material which may then be severed by rotating and axially translating the cutting blade.
The use of such atherectomy catheters has been limited primarily to removal of non-calcified stenotic material. Not infrequently however, an interventionist (physician) is confronted with a need to remove tissue including calcified deposits. The hardness of these deposits can be comparable to that of the material used to make the current cutting blade. Therefore, attempts to use atherectomy catheters to remove calcified tissue result in the cutting edge becoming rounded and dulled and is thereby rendered ineffective to remove non-calcified (soft) tissue.
What is needed is a cutting blade which is effective for cutting soft tissue.
What is also needed is a cutting blade durable enough to retain its soft tissue cutting ability when used to remove calcified tissue.
What is also needed is a cutting blade made of a material hard enough not to break.
Finally, what is needed is a cutting blade that is biocompatible.